The Mass Spectrometry Laboratory of the University of Texas Health Science Center at San Antonio functions as a multi-user support service for the Health Science Center and for the Southwest Research Consortium. Investigators from these institutions, involved in many different areas of biomedical research, utilize this facility. Currently, there are two Hewlett-Packard 5982 quadrupoles mass spectrometers and a Finnigan-MAT 212 magnetic sector instrument. One of the quadrupoles is used for direct insertion probe EI samples and packed column GC-MS analyses. The other quadrupole has been modified for thermospray HPLC-MS. The magnetic sector instrument is used primarily for FAB and non- routine capillary GC-MS (EI or CI). Less frequently, DCI and HPLC- MS (belt interface) are performed. quadrupole mass spectrometers were manufactured in 1975 and are now obsolete, both in the nature of their design and in the availability of parts and service. Hewlett-Packard no longer offers service contracts on these units, and many of the parts are not being made anymore. A new mass spectrometer is needed at this institution to: 1) assume the routine analyses currently being performed on the Hewlett-Packard quadrupole; 2) provide the capability for chemical ionization with negative ion detection. The first function will preserve the current status and is essential for projects requiring EI-GC-MS and direct insertion probe analyses. The second function will provide access to a technique of superior sensitivity and selectivity, which is critical to facilitate further progress in numerous ongoing investigations. A secondary aspect of this is proposal is upgrading the data system on the magnetic sector instrument. The current arrangement for data storage, which includes a 5 mb fixed disk and 5 mb removable cartridges, is restrictive in the number of spectra which can be preserved and is both unwieldy and laborious to use for file manipulation. Furthermore, the Nova 4C computer cannot acquire data at a fast enough rate to perform medium resolution capillary GC-MS. It is, therefore, essential that a new quadrupole mass spectrometer be obtained to perform daily service analyses and to provide highly sensitive NCI measurements. The purchase of a new quadrupole, along with upgrading of the data system on the magnetic sector instrument, will significantly enhance the probability for success of a multitude of research projects at this institution